I think CKEditor widget is a good replacement. RichText suite is not been updated since 2013 so not sure if this widget is still being maintained.
Hope this helps!
See this might be helpful
You are working on very old version of Mendix. To be confirmed that the widget works as intended, you should download few widgets from app store for “text editor” and see what works best.
You can also do Google Search to find if you get suitable Mendix widget on github, which you will have to download and import in the project manually.